A strap retractor assembly which is presently in use for a vehicular seat belt arrangement includes a tension lock mechanism for preventing a retaining strap from being tightly fitted on the seat occupant's body. Such a tension lock mechanism operates in cooperation with a solenoid operated actuator responsive to engagement between a tongue or male member and a buckle or female member which form part of the seat belt arrangement. When the tongue member is inserted into the buckle with the retaining strap withdrawn from the retractor assembly and fitted to the seat occupant, the solenoid-operated actuator is initiated into motion to prohibit the retaining strap from being retracted into the retractor assembly beyond a predetermined limit. A recently proposed version of such a tension lock mechanism has incorporated therein a slack-preventive feature by virtue of which the retaining strap once fitted tautly on the seat occupant's body is prohibited from being retracted into the retractor assembly in an adequately slackened condition. A slack-preventive tension lock mechanism of this nature is shown in, for example, Japanese Patent Application No. 52-132280.
The tension lock mechanism of such a prior-art strap retractor assembly is composed of mechanical members and elements such as gears and links and is for this reason responsible for the large-sized, intricate construction of the retractor assembly. The present invention contemplates an improved strap retractor assembly eliminating such a drawback.